Projectiles currently used for the M203/M320 include the M433 High Explosive Dual Purpose Round, M406 High Explosive Round, M583A1 Star Parachute Round, M585 White Star Cluster Round, M713 Ground Marker Round, M781 Practice Round, M651 CS Round and M576 Buckshot Round. The M203 is not a standalone gun. It must be attached to an M16 or M4 rifle, for instance, and fires a family of 40 mm low velocity projectile rounds. In order to load a 40 mm round into an M203, the forward sleeve of the gun tube is slid forward, and a 40 mm round is pushed into the sleeve. The sleeve is then slid backwards and locked into position, ready to fire. The barrel of the M203 is rifled, which spins up the projectile as it travels down the barrel tube, and the projectile leaves the gun tube with a high spin rate.
The 40 mm cartridge case is typically not reused or recycled after firing. If the cartridge case gets stuck in the gun tube, there is a tool to help the war-fighter push it from the tube. The M320 fires the same 40 mm low velocity ammunition as the M203. There are several improvements that the M320 has compared to the M203. The M320 has stand alone single shot capability and may be fired by the war-fighter without attaching to a gun. It also has the capability to be attached to and fired from the M16/M4 rifle, similarly to the M203. A major improvement of the M320 is the ability of the firing tube to open sideways. By opening sideways, longer ammunition can be loaded into the M320 gun tube as compared to loading in an M203. While the approximate maximum length of the projectile is approximately five inches in the M203, projectiles several inches longer can be loaded into an M320. Both M203 and M320 have rifled barrels which induce spinning in the projectile as it travels through the gun tube.
There exists a great need to eliminate projectile spinning, when fired from M203 or M320 Grenade Launcher guns. To permit increased accuracy and precision hits on targets as far range as beyond 1000 meters (a goal which is sought) it is necessary to provide projectile guidance, navigation and/or control subsystem components within the projectiles. However, guidance, navigation and control subsystems cannot function properly if the projectile were spinning at any appreciable revolution rate. Guided ammunition would need to have no spin (or very little spin) so that the seeker or camera therein, e.g., can see the target clearly while in flight. The conventional M203 or M320 Grenade Launcher guns launch spinning low velocity 40 mm projectiles because the Grenade Launcher tube barrels have internal rifling intended to spin up the projectiles (at approximately 1800 revolutions per second) for stabilization of flight. Clearly then, a way must be found to avoid this spin which is inherent in conventional M203 or M320 Grenade Launcher guns.